Plastic Comb "gauge" (distance between the holes)

I have been looking at plastic comb binders and I have found some apparently designed for letter-size (8 1/2 x 11) paper and some for A4 paper. I see that the letter-size combs (11" long) need 19 holes and the A4 combs need 21 holes. I know that A4 paper is almost 3/4" longer than letter size, so this might be the only reason for the 2 extra holes, but I am wondering if the holes are all the same distance apart. For instance if I punch a letter-size sheet with the longer 21-hole punching machine, will the letter-size combs fit? I hope I made that clear.

@casaerwin - I am going to suggest that yes, the distance between the combs would be the same. The same binding machine should be able to handle letter size (8-1/2 x 11), A4, and legal sized paper (8-12 x 14). Where the paper is positioned on the binding machine changes with how long it is, with notches on the machine itself to indicate where. So the distance between top and bottom combs and edges of paper may be different. You would want to punch the letter sized closer to the top of the paper so that you don't end up with a half hole at the bottom. I used a small punch machine for years before I started cutting with a die cutter:

PS - all my combs were the same size, so I just snipped the excess off. You could do that too.

If the holes are the same distance apart, that shoulln't be necessary. I will just use the letter size combs. Snipping off the excess was what I was planning as a plan B if the holes are not the same distance apart.

@Crazy_Mr_Zing - yes there would be, a difference for European sizes...but what is the difference between the A4 21 rings and letter at 19 rings? I could not find this information in a quick search it did.